The present invention relates to the field of orthodontics, and in particular to orthodontic brackets. In a related aspect, the invention relates to orthodontic methods and materials for the treatment of impacted teeth.
Orthodontia generally involves the treatment of malocclusions by the use of fixed appliances such as brackets and archwires. The teeth can be initially leveled by the use of an archwire of standardized archform and a given coefficient of elasticity. Later, heavier archwires can be substituted to perform root movements necessary for achieving optimal results.
A wide variety of types and styles of orthodontic brackets are available today, including those available from 3M Unitek (e.g., xe2x80x9cVictoryxe2x80x9d series brackets, as described in U.S. Pat. No. 5,395,237), and from Ormco Corporation. Ormco, for instance, markets its xe2x80x9cminidiamondxe2x80x9d line of brackets, which are described as being related to U.S. Pat. No. 4,415,330. The ""330 patent provides an orthodontic bracket assembly adapted for use with an arch wire in straightening a tooth having a crown long axis preferably disposed at a particular angle with respect to an occlusal plane.
When dealing with a malocclusion that involves one or more impacted teeth, various modifications or additional steps must be made to the general procedure. The treatment of impacted teeth typically includes surgical exposure followed by excision, spontaneous eruption or, more commonly, orthodontic traction. See, generally, xe2x80x9cTreatment Strategyxe2x80x9d, Chapter 4, pp 43-53 in The Orthodontic Treatment of Impacted Teeth, Adrian Becker, Mosby 1998.
The ectopic eruption and impaction of the permanent maxillary canine is a frequently encountered clinical problem whose treatment requires the cooperation of several dental specialties, particularly oral surgery and orthodontics. The incidence of this problem is between one percent and two percent of the population, with palatal impaction occurring in about 85% of the cases and buccal impaction in about 15% of the cases.
The cause of impaction is considered to be multifactorial, with local causes being the most common. These would include tooth size-arch length discrepancies, prolonged retention or early loss of deciduous canines, abnormal position of the tooth germ, alveolar cleft, cystic or neoplastic change, root dilaceration, and iatrogenic idiopathic reasons.
The management options for impacted canines depend on the type of impaction (e.g., either buccal or palatal), and the severity of the transplantation, or exposure, with or without orthodontic traction to align the malpositioned tooth. For unerupted teeth, the preferred option is surgical exposure and alignment by traction. Impacted teeth may also erupt ectopically and not need surgical intervention. They would, however, likely still require orthodontic guidance to achieve correct arch positions.
Orthodontic traction, and in particular, the use of attachments in connection with impacted teeth, has evolved over the years. Prior to the 1960""s, as described in Becker, it was common to use a lasso wire twisted lightly around an impacted canine. The lasso has since become obsolete, in large part because of the inevitable tendency of the lasso to settle at the narrowest diameter of the tooth, and the frequency of gingival irritation.
Several systems were then developed based on the use of threaded pins. These methods have also not met with widespread use, in view of the difficulties encountered in accessing impacted teeth, the desirability of limiting surgical exposure, and the risk of entering the pulp.
Standard preformed orthodontic bands have been used as well, including Edgewise, Begg and other orthodontic brackets. As explained in Becker, such brackets provide sophisticated designs of attachment that enable the orthodontist to perform any type of movement on a tooth in the three planes of space. It is not possible, however, to achieve more than tipping, extrusion, and some rotation, at least until the bracket reaches and fully engages the arch wire. In turn, the efficacy of such brackets in performing traction is no greater than the use of simple eyelets, as described below. Also, in view of the size and profile of such brackets, they can create irritation and interference when used in such applications.
One current approach that is employed today for the movement of impacted teeth, as described in Becker, includes the use of an eyelet, welded to a band material and used in conjunction with a mesh backing. The relatively small size and low profile allows the eyelet to be positioned in a midbuccal position of even awkwardly positioned teeth, and in a manner that is less irritating to the surrounding tissue. For these reasons, Becker recommends that a small eyelet be used as an initial attachment, at the time of surgery, to be removed (and replaced with a standard bracket) once the tooth has progressed to the point where it comes into close proximity to the archwire. A bonded xe2x80x9cbuttonxe2x80x9d is commonly also used in this situation. Retention of the elastic ligature is unreliable, however, and the edges can be sharp and irritating for the patient. Unfortunately, elastic modular traction cannot be used alone with the eyelet design to complete orthodontic treatment. Later, a more sophisticated bracket can be used for more intricate root manipulations, including rotating, uprighting, and torqueing.
Along similar lines, Northcutt (U.S. Pat. No. 3,835,538) describes an orthodontic onlay which is cemented directly to an impacted tooth to aid in exerting corrective traction thereon. A curved base surface has a curvature substantially the same as an incisal portion of the tooth involved. The onlay has a series of openings or recesses leading from that surface toward the opposite surface for receiving and holding cement, thereby increasing the bond between the tooth and the onlay when the cement is applied. Bonding strength is increased further by plasma processing the surface, especially when the onlay is made from plastic. On its opposite surface the onlay has means for attaching a ligature. The specialized orthodontic onlay is said to be made of plastic and secured by cement (such as a suitable epoxy cement) directly to the tooth. By use of the onlay, the patent proposes that it would no longer be necessary to remove bone from the entire crown. Instead, a small window incision is sufficient to gain access and to enable the desired traction. The xe2x80x9cmeansxe2x80x9d for attaching a ligature are depicted (e.g., in FIG. 2 thereof) as either a plastic loop (25) or a metal member (26), each analogous in shape to a single eyelet.
A significant aspect, and focus, of the onlay described in Northcutt appears to be the method of cementing it onto the tooth. The patent describes the problem of achieving sufficient adhesion to enable small articles to transmit a substantial amount of traction. It addresses that problem by applying cement to the onlay, with the aid of a special plasma-processed surface and a series of openings from the surface to be cemented. The openings, and additional cement, were said to enable a strong xe2x80x98bondingxe2x80x99 force to be applied. For whatever reason, however, to the best of Applicant""s knowledge, no such onlay is commercially available today.
Other common approaches, presently employed by Applicant and others, involve the use of a bonded lingual button or makeshift brackets. Conventional brackets, however, tend to have wide, rigid bases as well as a wide, sharp and high profile which can cause irritation as the tooth is drawn through the soft tissues. In turn, it is often difficult or impossible to bond a conventional bracket to the necessary position on an impacted tooth.
While the eyelet described by Becker, and such other approaches, have gained some acceptance, they continue to suffer from considerable drawbacks. Often, for instance, the elastic thread can become disengaged due to poor retention on the eyelet or bracket. Wire chains have similar problems, and have a tendency to pull the bonded bracket off when activated. Hence, these techniques remain cumbersome, inefficient and of questionable utility.
What is clearly needed are new materials and methods for treating impacted teeth, in a manner that avoids the shortcomings of present techniques.